T-3 Planet

A T-3 Planet is a world in Spore that has a completed ecosystem which consists of 3 shrubs, 3 bushes, 3 trees, 6 herbivores, and 3 carnivores/omnivores. A T-3's atmospheric level and temperature are optimal for hosting life. On the terraforming HUD, this is shown by the dot being right in the centre of the graded circle, which will be completely green when the planet is 'maxed out'. In summary, T-3 worlds are generally the greenest planets, with minimal amounts of bare terrain, and swathes of forests, alongside an abundance of fauna.
Category 3 Planets are the rarest worlds in Spore. They are often either that of the players homeworld, another sentient species homeworld, storybook planets, or worlds that you have personally terraformed. Although T-3s can be found that don't fit these categories, they will almost always be claimed, as the provide the most resources for an empire.

A T-3 planet can support 3 colonies each with no atmospheric shielding bubble to hold in air and the maximum number of buildings, including turrets. The exception to this are homeworlds, which can have more than three colonies. Most, but not all home planets are T-3. The players homeplanet will always be T-3 throughout the duration of the game across 4 stages of development (a glitch can happen were cell no cells spawn making an unfulfilled ecosystem). T-3 planets are argueably the most important to an empire as they can create spice faster and in larger quantities than any other level of planet, (except T-2 Planets with no turrets, however they have less cities) especially captured homeworlds with more than 5 cities.
T-3 planets that have been colonised tend to also be the most defended worlds, as the maximum amount of settlements can be placed with the maximum amount of turrets. This, combined with an Uber Turret, makes T-3 colonies almost impossible for an enemy empire to capture, with the excepion being The Grox.

An enemies homeworld is typically a T-3 world, with the exception of the Grox and Monolith-raised civilizations. T-3 Worlds can be tricky to capture, as empires typically maximize their colonies with buildings and turrets. These colonies also release numerous spaceships for their defence.

They also have more colonies then the usual three colonies, and you can have them by conquering or setting up a Trade Route.